HSC 12th Maths June 2026 Board Paper Solution (J-276) | Class 12 Mathematics & Statistics Answer Key
Are you looking for the complete, step-by-step solutions for the HSC 12th Standard Mathematics and Statistics June 2026 Board Question Paper (Subject Code: J-276) held on 24/06/2026? Below is the full, solved answer key covering Section A, Section B, Section C, and Section D prepared strictly according to the Maharashtra State Board marking scheme to help Class 12 students score full marks.
HSC 12th Maths (Arts & Science) June 2026 Board Paper Solution
SECTION - A
Q. 1. Select and write the correct answer of the following multiple choice type of questions:
-
If A = {1, 2, 3, 4, 5} then which of the following is not true?
Solution: (c) $x \in A, x+6 \ge 9$
Explanation: If we take $x = 1$ from set A, $1 + 6 = 7$, which is not greater than or equal to 9. Thus, the statement is false.
-
The value of $\sin[\sin^{-1}(-\frac{1}{\sqrt{2}}) - 3 \sin^{-1}(\frac{\sqrt{3}}{2})] =$
Solution: (b) $\frac{1}{\sqrt{2}}$
Explanation:
$\sin^{-1}(-\frac{1}{\sqrt{2}}) = -\frac{\pi}{4}$
$\sin^{-1}(\frac{\sqrt{3}}{2}) = \frac{\pi}{3}$
Expression becomes: $\sin(-\frac{\pi}{4} - 3(\frac{\pi}{3})) = \sin(-\frac{\pi}{4} - \pi) = \sin(-\frac{5\pi}{4}) = \frac{1}{\sqrt{2}}$. -
If $\hat{p}, \hat{q}, \hat{r}$ are mutually perpendicular unit vectors and form a right handed triplet then the value of $\hat{p}\cdot(\hat{q}\times\hat{r}) + \hat{q}\cdot(\hat{p}\times\hat{r}) + \hat{r}\cdot(\hat{p}\times\hat{q}) = $
Solution: (c) 1
Explanation: For a right-handed triplet of mutually perpendicular unit vectors:
$\hat{q} \times \hat{r} = \hat{p}$ (so $\hat{p}\cdot\hat{p} = 1$)
$\hat{p} \times \hat{r} = -\hat{q}$ (so $\hat{q}\cdot(-\hat{q}) = -1$)
$\hat{p} \times \hat{q} = \hat{r}$ (so $\hat{r}\cdot\hat{r} = 1$)
Sum = $1 - 1 + 1 = 1$. -
The Cartesian equation of the line passing through the points A(3, 4, -1) and B(2, -1, 3) is:
Solution: (a) $\frac{x-3}{1} = \frac{y-4}{5} = \frac{z+1}{-4}$
Explanation: Direction ratios (DRs) of AB = (2-3, -1-4, 3-(-1)) = (-1, -5, 4). Equivalent DRs are (1, 5, -4). Using point A(3,4,-1), the equation is $\frac{x-3}{1} = \frac{y-4}{5} = \frac{z+1}{-4}$.
-
If $y = \log_x a$ then $\frac{dy}{dx} =$
Solution: (a) $\frac{-\log a}{x(\log x)^2}$
Explanation: Using the change of base rule, $y = \frac{\log a}{\log x} = \log a \cdot (\log x)^{-1}$. Differentiating with respect to $x$: $\frac{dy}{dx} = \log a \cdot (-1)(\log x)^{-2} \cdot \frac{d}{dx}(\log x) = \log a \cdot \frac{-1}{(\log x)^2} \cdot \frac{1}{x} = \frac{-\log a}{x(\log x)^2}$.
-
If $f(x) = \frac{\sin^{-1}x}{\sqrt{1-x^2}}$ and $g(x) = e^{\sin^{-1}x}$ then $\int f(x)\cdot g(x)dx = $
Solution: (b) $e^{\sin^{-1}x}(\sin^{-1}x - 1) + c$
Explanation: We need to evaluate $\int \frac{\sin^{-1}x}{\sqrt{1-x^2}} e^{\sin^{-1}x} dx$. Let $t = \sin^{-1}x$, then $dt = \frac{1}{\sqrt{1-x^2}} dx$. The integral becomes $\int t e^t dt$. Using integration by parts: $t \int e^t dt - \int (1 \cdot e^t) dt = t e^t - e^t + c = e^t(t - 1) + c$. Substituting back $t = \sin^{-1}x$, we get $e^{\sin^{-1}x}(\sin^{-1}x - 1) + c$.
-
The area bounded by the line $y=2x$, X-axis and the lines $x=-1$, $x=4$ is _____ sq. units.
Solution: (b) 17
Explanation: The area is given by $\int_{-1}^{4} |y| dx = \int_{-1}^{0} |2x| dx + \int_{0}^{4} |2x| dx$. Since $2x$ is negative for $x < 0$, we have $\int_{-1}^{0} (-2x) dx + \int_{0}^{4} (2x) dx$. Evaluating the integrals: $[-x^2]_{-1}^{0} + [x^2]_{0}^{4} = (0 - (-1)) + (16 - 0) = 1 + 16 = 17$ sq. units.
-
In a Binomial Distribution, $E(X)=6$, $Var(X)=4.2$ then the value of n is _____
Solution: 20
Explanation: For a Binomial Distribution, Mean $E(X) = np = 6$ and Variance $Var(X) = npq = 4.2$. Dividing variance by mean: $\frac{npq}{np} = \frac{4.2}{6} \Rightarrow q = 0.7$. Since $p = 1 - q$, we get $p = 1 - 0.7 = 0.3$. Substituting $p$ back into the mean equation: $n(0.3) = 6 \Rightarrow n = \frac{6}{0.3} = 20$.
Q. 2. Answer the following questions:
-
Write the dual of $p \wedge \sim q$
Solution: $p \vee \sim q$
Explanation: To write the dual of a logical statement, we replace the conjunction symbol ($\wedge$) with the disjunction symbol ($\vee$) and vice versa. Negations ($\sim$) remain unchanged.
-
What is the distance of point (3, 5, 6) from XZ plane?
Solution: 5 units
Explanation: The perpendicular distance of any point $(x, y, z)$ from the XZ plane is given by the absolute value of its y-coordinate, $|y|$. Here, the y-coordinate is 5, so the distance is $|5| = 5$ units.
-
The displacement of a particle at time t is given by $S = 3t^2 + 4t + 1$. Find its velocity at time t.
Solution: $v = 6t + 4$
Explanation: Velocity ($v$) is the rate of change of displacement ($S$) with respect to time ($t$).
$v = \frac{dS}{dt} = \frac{d}{dt}(3t^2 + 4t + 1) = 6t + 4$. -
Write the order of differential equation $(\frac{d^2y}{dx^2})^{\frac{5}{2}} = \sqrt[3]{\frac{dy}{dx}}$
Solution: Order = 2
Explanation: The order of a differential equation is the order of the highest derivative present in the equation. Here, the highest derivative is $\frac{d^2y}{dx^2}$, which is a second-order derivative. Therefore, the order is 2.
SECTION - B
Attempt any EIGHT of the following questions:
Q. 3. Construct the switching circuit for the statement $(\sim p \wedge q) \vee (p \wedge \sim r)$.
Solution:
Let,
$p$: Switch $S_1$ is closed.
$q$: Switch $S_2$ is closed.
$r$: Switch $S_3$ is closed.
$\sim p$: Switch $S_1'$ is closed.
$\sim r$: Switch $S_3'$ is closed.
The given logical statement pattern is $(\sim p \wedge q) \vee (p \wedge \sim r)$.
- The term $(\sim p \wedge q)$ indicates that switches $S_1'$ and $S_2$ are connected in series.
- The term $(p \wedge \sim r)$ indicates that switches $S_1$ and $S_3'$ are connected in series.
- The disjunction ($\vee$) between the two brackets indicates that these two series branches are connected in parallel to each other.
Q. 4. Find the matrix of cofactors of matrix $\begin{bmatrix} 5 & 2 \\ -1 & 6 \end{bmatrix}$
Solution:
Let the given matrix be $A = \begin{bmatrix} 5 & 2 \\ -1 & 6 \end{bmatrix}$
Here, the elements of the matrix are:
$a_{11} = 5, a_{12} = 2$
$a_{21} = -1, a_{22} = 6$
The cofactors $C_{ij}$ are calculated using the formula $C_{ij} = (-1)^{i+j} M_{ij}$, where $M_{ij}$ is the minor of the element $a_{ij}$.
- $C_{11} = (-1)^{1+1} (6) = 1 \times 6 = 6$
- $C_{12} = (-1)^{1+2} (-1) = -1 \times -1 = 1$
- $C_{21} = (-1)^{2+1} (2) = -1 \times 2 = -2$
- $C_{22} = (-1)^{2+2} (5) = 1 \times 5 = 5$
Therefore, the matrix of cofactors is:
$\begin{bmatrix} C_{11} & C_{12} \\ C_{21} & C_{22} \end{bmatrix} = \begin{bmatrix} 6 & 1 \\ -2 & 5 \end{bmatrix}$
Q. 5. Find the general solution of equation $\cos 5\theta = \frac{1}{2}$.
Solution:
Given equation is $\cos 5\theta = \frac{1}{2}$
We know that $\cos(\frac{\pi}{3}) = \frac{1}{2}$
Therefore, $\cos 5\theta = \cos(\frac{\pi}{3})$
The general solution for $\cos x = \cos \alpha$ is $x = 2n\pi \pm \alpha$, where $n \in Z$.
Here, $x = 5\theta$ and $\alpha = \frac{\pi}{3}$.
$5\theta = 2n\pi \pm \frac{\pi}{3}$, where $n \in Z$
Dividing both sides by 5, we get:
$\theta = \frac{2n\pi}{5} \pm \frac{\pi}{15}$, where $n \in Z$
This is the required general solution.
Q. 6. Find the value of k, if $2x+y=0$ is one of the lines represented by $3x^2+kxy+2y^2=0$.
Solution:
The given combined equation of the lines is:
$3x^2 + kxy + 2y^2 = 0$
Comparing this with the standard homogeneous equation $ax^2 + 2hxy + by^2 = 0$, we get:
$a = 3$, $2h = k$, and $b = 2$
The corresponding auxiliary equation is $bm^2 + 2hm + a = 0$.
Substituting the values of $a$, $2h$, and $b$, we get:
$2m^2 + km + 3 = 0$ ...(i)
We are given that $2x + y = 0$ is one of the lines represented by the combined equation.
Writing this in the slope-intercept form ($y = mx + c$), we get:
$y = -2x$
Therefore, the slope of this line is $m = -2$.
Since this line is a part of the given combined equation, its slope $m = -2$ must satisfy the auxiliary equation (i).
Substitute $m = -2$ in equation (i):
$2(-2)^2 + k(-2) + 3 = 0$
$2(4) - 2k + 3 = 0$
$8 - 2k + 3 = 0$
$11 - 2k = 0$
$2k = 11$
$k = \frac{11}{2}$
Therefore, the value of $k$ is $\frac{11}{2}$.
Q. 7. If $\overline{a}$, $\overline{b}$, $\overline{c}$ are the position vectors of points A, B, C respectively and $10\overline{a} = 7\overline{b} + 3\overline{c}$ then find the ratio in which the point C divides the line segment AB.
Solution:
Given equation is:
$10\overline{a} = 7\overline{b} + 3\overline{c}$
We need to find the ratio in which point C divides the line segment AB. Let's express $\overline{c}$ in terms of $\overline{a}$ and $\overline{b}$.
$3\overline{c} = 10\overline{a} - 7\overline{b}$
Dividing both sides by 3, we get:
$\overline{c} = \frac{10\overline{a} - 7\overline{b}}{3}$
This can be written in the form of the section formula for external division:
$\overline{c} = \frac{-7\overline{b} + 10\overline{a}}{-7 + 10}$
Comparing this with the section formula $\overline{c} = \frac{m\overline{b} + n\overline{a}}{m + n}$, we get:
$m = -7$ and $n = 10$
The ratio is $m : n = -7 : 10$.
Since the ratio is negative, the division is external. We can also compare it directly with the external division formula $\overline{c} = \frac{m\overline{b} - n\overline{a}}{m - n}$:
$\overline{c} = \frac{7\overline{b} - 10\overline{a}}{7 - 10} = \frac{10\overline{a} - 7\overline{b}}{3}$
Here, $m = 7$ and $n = 10$.
Therefore, the point C divides the line segment AB externally in the ratio 7:10.
Q. 8. Find the angle between the lines $\overline{r}=(\hat{i}+2\hat{j}+3\hat{k})+\lambda(2\hat{i}-\hat{j}+\hat{k})$ and $\overline{r}=(\hat{i}+2\hat{j}+3\hat{k})+\mu(\hat{i}+2\hat{j}+\hat{k})$
Solution:
Let the given lines be:
$L_1: \overline{r} = \overline{a}_1 + \lambda\overline{b}_1$
$L_2: \overline{r} = \overline{a}_2 + \mu\overline{b}_2$
Comparing the given equations with standard forms, the direction vectors of the lines are:
$\overline{b}_1 = 2\hat{i} - \hat{j} + \hat{k}$
$\overline{b}_2 = \hat{i} + 2\hat{j} + \hat{k}$
Let $\theta$ be the acute angle between the two lines. The formula for the angle is:
$\cos \theta = \frac{|\overline{b}_1 \cdot \overline{b}_2|}{|\overline{b}_1| |\overline{b}_2|}$
Now, let's find the dot product $\overline{b}_1 \cdot \overline{b}_2$:
$\overline{b}_1 \cdot \overline{b}_2 = (2\hat{i} - \hat{j} + \hat{k}) \cdot (\hat{i} + 2\hat{j} + \hat{k})$
$\overline{b}_1 \cdot \overline{b}_2 = (2)(1) + (-1)(2) + (1)(1)$
$\overline{b}_1 \cdot \overline{b}_2 = 2 - 2 + 1 = 1$
Next, find the magnitudes of the direction vectors:
$|\overline{b}_1| = \sqrt{(2)^2 + (-1)^2 + (1)^2} = \sqrt{4 + 1 + 1} = \sqrt{6}$
$|\overline{b}_2| = \sqrt{(1)^2 + (2)^2 + (1)^2} = \sqrt{1 + 4 + 1} = \sqrt{6}$
Substitute these values into the formula:
$\cos \theta = \frac{|1|}{\sqrt{6} \times \sqrt{6}}$
$\cos \theta = \frac{1}{6}$
Therefore, the angle between the lines is:
$\theta = \cos^{-1}(\frac{1}{6})$
Q. 9. Test whether the function $f(x) = x - \frac{1}{x}$, $x \in R, x \ne 0$ is increasing or decreasing.
Solution:
The given function is $f(x) = x - \frac{1}{x}$
Differentiating with respect to $x$, we get:
$f'(x) = \frac{d}{dx}(x) - \frac{d}{dx}(\frac{1}{x})$
$f'(x) = 1 - (-\frac{1}{x^2})$
$f'(x) = 1 + \frac{1}{x^2}$
For any real number $x \ne 0$, the square of $x$ is always positive, i.e., $x^2 > 0$.
Therefore, $\frac{1}{x^2} > 0$
Adding 1 to both sides:
$1 + \frac{1}{x^2} > 1 > 0$
This means $f'(x) > 0$ for all $x \in R, x \ne 0$.
Hence, the given function $f(x)$ is strictly increasing for all $x \in R, x \ne 0$.
Q. 10. Evaluate: $\int_{-1}^{1}|x|dx$
Solution:
Let $I = \int_{-1}^{1}|x|dx$
We know the definition of the absolute value function:
$|x| = -x$ for $x < 0$
$|x| = x$ for $x \ge 0$
We split the definite integral at $x = 0$:
$I = \int_{-1}^{0} (-x) dx + \int_{0}^{1} (x) dx$
Integrating both terms:
$I = \left[ -\frac{x^2}{2} \right]_{-1}^{0} + \left[ \frac{x^2}{2} \right]_{0}^{1}$
Applying the limits:
$I = \left( 0 - \left(-\frac{(-1)^2}{2}\right) \right) + \left( \frac{1^2}{2} - 0 \right)$
$I = \left( 0 - \left(-\frac{1}{2}\right) \right) + \left( \frac{1}{2} \right)$
$I = \frac{1}{2} + \frac{1}{2}$
$I = 1$
(Alternatively, since $f(x) = |x|$ is an even function, $\int_{-1}^{1}|x|dx = 2\int_{0}^{1}xdx = 2 \left[ \frac{x^2}{2} \right]_{0}^{1} = 2(\frac{1}{2}) = 1$)
Question 11
Evaluate: ∫ x log x dx
Solution:
Let I = ∫ x log x dx
We solve this using the method of integration by parts. The formula is:
∫ u · v dx = u ∫ v dx - ∫ [ (du/dx) · ∫ v dx ] dx
According to the LIATE rule (Logarithmic, Inverse, Algebraic, Trigonometric, Exponential), we choose our functions as follows:
- u = log x (Logarithmic function)
- v = x (Algebraic function)
Applying the integration by parts formula:
I = (log x) ∫ x dx - ∫ [ (d/dx (log x)) · ∫ x dx ] dx
Now, compute the individual derivatives and integrals:
- ∫ x dx = x² / 2
- d/dx (log x) = 1 / x
Substitute these back into the equation:
I = (log x) · (x² / 2) - ∫ [ (1 / x) · (x² / 2) ] dx
I = (x² / 2) log x - (1 / 2) ∫ x dx
I = (x² / 2) log x - (1 / 2) · (x² / 2) + C
I = (x² / 2) log x - (x² / 4) + C
Where 'C' is the constant of integration.
Question 12
Find the area bounded by curve x² + y = 0, X-axis and lines x = 1 and x = 4.
Solution:
The equation of the given curve is:
x² + y = 0 ⇒ y = -x²
Required area (A) bounded by the curve, the X-axis, and the lines x = 1 and x = 4 is given by:
A = ∫14 |y| dx
A = ∫14 |-x²| dx
A = ∫14 x² dx
Integrating with respect to x:
A = [ x³ / 3 ]14
A = (4³ / 3) - (1³ / 3)
A = (64 / 3) - (1 / 3)
A = 63 / 3
A = 21 sq. units
Question 13
The probability distribution of r.v. X is as follows:
| X = x | 0 | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| P(X = x) | 0.1 | k | 2k | 2k | k |
Find : (i) k (ii) F(2)
Solution:
Since P(X = x) is the probability distribution of a random variable X, the sum of all probabilities is equal to 1:
∑ P(X = x) = 1
(i) To find k:
P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) = 1
0.1 + k + 2k + 2k + k = 1
0.1 + 6k = 1
6k = 1 - 0.1
6k = 0.9
k = 0.9 / 6
k = 0.15 (or 3/20)
(ii) To find F(2):
By definition of the cumulative distribution function (c.d.f.):
F(2) = P(X ≤ 2)
F(2) = P(X = 0) + P(X = 1) + P(X = 2)
F(2) = 0.1 + k + 2k
F(2) = 0.1 + 3k
Substituting k = 0.15:
F(2) = 0.1 + 3(0.15)
F(2) = 0.1 + 0.45
F(2) = 0.55 (or 11/20)
Question 14
Evaluate: ∫ [ ex(1 + x) / cos²(xex) ] dx
Solution:
Let I = ∫ [ ex(1 + x) / cos²(xex) ] dx
Use the method of substitution by putting:
xex = t
Differentiating both sides with respect to x using the product rule:
[ x · (d/dx (ex)) + ex · (d/dx (x)) ] dx = dt
(x ex + ex · 1) dx = dt
ex(1 + x) dx = dt
Substitute these values into the integral I:
I = ∫ (1 / cos² t) dt
I = ∫ sec² t dt
I = tan t + C
Resubstituting t = xex:
I = tan(xex) + C
Where 'C' is the constant of integration.
Section C
Question 15
Problem: Determine using a truth table whether the logical expression [(p ∨ q) ∧ ~p] ∧ ~q is a tautology, a contradiction, or a contingency.
Solution:
| p | q | ~p | ~q | p ∨ q | (p ∨ q) ∧ ~p | [(p ∨ q) ∧ ~p] ∧ ~q |
|---|---|---|---|---|---|---|
| T | T | F | F | T | F | F |
| T | F | F | T | T | F | F |
| F | T | T | F | T | T | F |
| F | F | T | T | F | F | F |
All the truth values in the last column are False (F).
Conclusion: The given statement pattern is a contradiction.
Question 16
Problem: Show that sin-1(3/5) + cos-1(12/13) = sin-1(56/65).
Solution:
Let sin-1(3/5) = x and cos-1(12/13) = y, where 0 < x, y < π/2.
Therefore, sin x = 3/5 and cos y = 12/13.
Using the trigonometric identity sin²θ + cos²θ = 1:
- cos x = √(1 - sin²x) = √(1 - (3/5)²) = √(1 - 9/25) = √(16/25) = 4/5
- sin y = √(1 - cos²y) = √(1 - (12/13)²) = √(1 - 144/169) = √(25/169) = 5/13
We know the compound angle formula:
sin(x + y) = sin x cos y + cos x sin y
sin(x + y) = (3/5)(12/13) + (4/5)(5/13)
sin(x + y) = (36/65) + (20/65)
sin(x + y) = 56/65
x + y = sin-1(56/65)
Resubstituting the values of x and y:
sin-1(3/5) + cos-1(12/13) = sin-1(56/65)
Hence proved.
Question 17
Problem: Given a triangle ABC with sides a = 10, b = 8, and c = 6, compute the values of (i) sin(C/2) and (ii) cos(B/2).
Solution:
Given: a = 10, b = 8, c = 6
First, find the semi-perimeter (s) of ΔABC:
2s = a + b + c = 10 + 8 + 6 = 24
s = 12
Now compute:
- s - a = 12 - 10 = 2
- s - b = 12 - 8 = 4
- s - c = 12 - 6 = 6
(i) To find sin(C/2):
By the half-angle formula:
sin(C/2) = √[ (s - a)(s - b) / (ab) ]
sin(C/2) = √[ (2 × 4) / (10 × 8) ]
sin(C/2) = √(8 / 80) = √(1 / 10)
sin(C/2) = 1 / √10
(ii) To find cos(B/2):
By the half-angle formula:
cos(B/2) = √[ s(s - b) / (ac) ]
cos(B/2) = √[ (12 × 4) / (10 × 6) ]
cos(B/2) = √(48 / 60) = √(4 / 5)
cos(B/2) = 2 / √5
Question 18
Problem: Determine with justification whether the four points A(1, 2, 1), B(2, -3, 4), C(3, 4, -5), and D(2, 3, -2) lie on the same plane.
Solution:
Let the position vectors of the given points be:
- a = î + 2ĵ + k̂
- b = 2î - 3ĵ + 4k̂
- c = 3î + 4ĵ - 5k̂
- d = 2î + 3ĵ - 2k̂
Find the vectors AB, AC, and AD:
- AB = b - a = (2 - 1)î + (-3 - 2)ĵ + (4 - 1)k̂ = î - 5ĵ + 3k̂
- AC = c - a = (3 - 1)î + (4 - 2)ĵ + (-5 - 1)k̂ = 2î + 2ĵ - 6k̂
- AD = d - a = (2 - 1)î + (3 - 2)ĵ + (-2 - 1)k̂ = î + ĵ - 3k̂
Now, evaluate the scalar triple product [AB AC AD]:
| | 1 | -5 | 3 | |
| | 2 | 2 | -6 | |
| | 1 | 1 | -3 | |
[AB AC AD] = 1( (2)(-3) - (-6)(1) ) - (-5)( (2)(-3) - (-6)(1) ) + 3( (2)(1) - (2)(1) )
[AB AC AD] = 1(-6 + 6) + 5(-6 + 6) + 3(2 - 2)
[AB AC AD] = 1(0) + 5(0) + 3(0) = 0
Since the scalar triple product [AB AC AD] = 0, the vectors AB, AC, and AD are coplanar.
Conclusion: Yes, the four points A, B, C, and D are coplanar.
Question 19
Problem: Calculate the shortest distance between the parallel lines x/2 = y/(-1) = z/2 and (x + 1)/2 = (y - 1)/(-1) = (z + 1)/2.
Solution:
The equations of the given parallel lines are:
- Line 1: x/2 = y/(-1) = z/2
- Line 2: (x + 1)/2 = (y - 1)/(-1) = (z + 1)/2
From the equations of the lines:
- Position vector of a point on the first line: a1 = 0î + 0ĵ + 0k̂
- Position vector of a point on the second line: a2 = -î + ĵ - k̂
- Direction vector parallel to both lines: b = 2î - ĵ + 2k̂
Now, compute a2 - a1:
a2 - a1 = -î + ĵ - k̂
Next, compute the cross product (a2 - a1) × b:
| | î | ĵ | k̂ | |
| | -1 | 1 | -1 | |
| | 2 | -1 | 2 | |
(a2 - a1) × b = î(2 - 1) - ĵ(-2 + 2) + k̂(1 - 2)
(a2 - a1) × b = î - 0ĵ - k̂ = î - k̂
Find the magnitudes:
- |(a2 - a1) × b| = √(1² + 0² + (-1)²) = √2
- |b| = √(2² + (-1)² + 2²) = √(4 + 1 + 4) = √9 = 3
The distance (d) between the two parallel lines is given by:
d = |(a2 - a1) × b| / |b|
d = (√2 / 3) units
Question 20
Problem: Determine the vector equation of the plane passing through the points A(2, 1, 1), B(0, 2, 3), and C(4, 5, 6).
Solution:
Let the position vectors of points A, B, and C be a, b, and c respectively:
- a = 2î + ĵ + k̂
- b = 0î + 2ĵ + 3k̂
- c = 4î + 5ĵ + 6k̂
Then:
- AB = b - a = (0 - 2)î + (2 - 1)ĵ + (3 - 1)k̂ = -2î + ĵ + 2k̂
- AC = c - a = (4 - 2)î + (5 - 1)ĵ + (6 - 1)k̂ = 2î + 4ĵ + 5k̂
A normal vector to the plane is given by n = AB × AC:
| | î | ĵ | k̂ | |
| | -2 | 1 | 2 | |
| | 2 | 4 | 5 | |
AB × AC = î(5 - 8) - ĵ(-10 - 4) + k̂(-8 - 2)
AB × AC = -3î + 14ĵ - 10k̂
Now calculate a · (AB × AC):
a · (AB × AC) = (2î + ĵ + k̂) · (-3î + 14ĵ - 10k̂)
a · (AB × AC) = 2(-3) + 1(14) + 1(-10) = -6 + 14 - 10 = -2
The vector equation of the plane passing through three points is:
r · (AB × AC) = a · (AB × AC)
r · (-3î + 14ĵ - 10k̂) = -2
Or equivalently:
r · (3î - 14ĵ + 10k̂) = 2
Question 21
Problem: Given y = log[ (x + √(x² + a²)) / (√(x² + a²) - x) ], find dy/dx.
Solution:
Given:
y = log[ (x + √(x² + a²)) / (√(x² + a²) - x) ]
Using the logarithmic property log(m / n) = log m - log n:
y = log(x + √(x² + a²)) - log(√(x² + a²) - x)
Differentiating both sides with respect to x:
dy/dx = [ 1 / (x + √(x² + a²)) ] · d/dx (x + √(x² + a²)) - [ 1 / (√(x² + a²) - x) ] · d/dx (√(x² + a²) - x)
dy/dx = [ 1 / (x + √(x² + a²)) ] · [ 1 + (2x / (2√(x² + a²))) ] - [ 1 / (√(x² + a²) - x) ] · [ (2x / (2√(x² + a²))) - 1 ]
dy/dx = [ 1 / (x + √(x² + a²)) ] · [ (√(x² + a²) + x) / √(x² + a²) ] - [ 1 / (√(x² + a²) - x) ] · [ (x - √(x² + a²)) / √(x² + a²) ]
dy/dx = [ 1 / √(x² + a²) ] - [ -(√(x² + a²) - x) / ( (√(x² + a²) - x) √(x² + a²) ) ]
dy/dx = [ 1 / √(x² + a²) ] + [ 1 / √(x² + a²) ]
dy/dx = 2 / √(x² + a²)
Question 22
Problem: A wire of total length 36 cm is bent into the shape of a rectangle. Find the dimensions of the rectangle so that its enclosed area is maximized.
Solution:
Let the length of the rectangle be x cm and the breadth of the rectangle be y cm.
Given that the perimeter of the rectangle is equal to the length of the wire (36 cm):
2(x + y) = 36
x + y = 18
y = 18 - x — (Equation 1)
Let A be the area of the rectangle:
A = x · y
A = x(18 - x)
A = 18x - x²
Differentiating A with respect to x:
dA/dx = 18 - 2x
Differentiating again with respect to x:
d²A/dx² = -2
For maximum or minimum area, put dA/dx = 0:
18 - 2x = 0
2x = 18 ⇒ x = 9
At x = 9, d²A/dx² = -2 < 0.
By the second derivative test, the area A is maximum when x = 9 cm.
Substituting x = 9 in Equation 1:
y = 18 - 9 ⇒ y = 9
Conclusion: For the area to be maximum, the dimensions of the rectangle are length = 9 cm and breadth = 9 cm.
Question 23
Problem: Verify Rolle's theorem for the polynomial function f(x) = x² - 5x + 9 on the interval [1, 4].
Solution:
Given function: f(x) = x² - 5x + 9 on x ∈ [1, 4].
Since f(x) is a polynomial function:
- f(x) is continuous on the closed interval [1, 4].
- f(x) is differentiable on the open interval (1, 4).
Now check the values of f(x) at the endpoints of the interval:
- f(1) = (1)² - 5(1) + 9 = 1 - 5 + 9 = 5
- f(4) = (4)² - 5(4) + 9 = 16 - 20 + 9 = 5
Here, f(1) = f(4) = 5.
Thus, all three conditions of Rolle's theorem are satisfied. Therefore, there exists at least one real number c ∈ (1, 4) such that f'(c) = 0.
Differentiating f(x) with respect to x:
f'(x) = 2x - 5
Put f'(c) = 0:
2c - 5 = 0
2c = 5 ⇒ c = 5/2 = 2.5
Since c = 2.5 ∈ (1, 4), Rolle's theorem is verified.
Question 24
Problem: Find the general solution of the differential equation x(dy/dx) - √(x² + y²) = y.
Solution:
Given differential equation:
x(dy/dx) - √(x² + y²) = y
x(dy/dx) = y + √(x² + y²)
dy/dx = [ y + √(x² + y²) ] / x — (Equation 1)
This is a homogeneous differential equation. Put y = vx.
Differentiating with respect to x:
dy/dx = v + x(dv/dx)
Substitute y = vx and dy/dx into Equation 1:
v + x(dv/dx) = [ vx + √(x² + v²x²) ] / x
v + x(dv/dx) = [ vx + x√(1 + v²) ] / x
v + x(dv/dx) = v + √(1 + v²)
x(dv/dx) = √(1 + v²)
Separating the variables:
[ 1 / √(1 + v²) ] dv = (1 / x) dx
Integrating both sides:
∫ [ 1 / √(1 + v²) ] dv = ∫ (1 / x) dx
log|v + √(1 + v²)| = log|x| + log|c|
log|v + √(1 + v²)| = log|cx|
v + √(1 + v²) = cx
Resubstituting v = y / x:
(y / x) + √(1 + y²/x²) = cx
[ y + √(x² + y²) ] / x = cx
y + √(x² + y²) = cx²
This is the required general solution.
Question 25
Problem: For a continuous random variable X with probability density function f(x) = x/8 for 0 < x < 4 (and 0 otherwise), find (i) the cumulative distribution function F(x), and (ii) the values of F(x) at x = 0.5 and x = 5.
Solution:
Given p.d.f. of continuous random variable X:
- f(x) = x / 8, for 0 < x < 4
- f(x) = 0, otherwise
(i) Expression for c.d.f. F(x):
By definition, F(x) = ∫-∞x f(t) dt.
- For x ≤ 0: F(x) = 0
- For 0 < x < 4:
F(x) = ∫0x (t / 8) dt = (1 / 8) [ t² / 2 ]0x = x² / 16
- For x ≥ 4: F(x) = 1
(ii) Values of F(x) at x = 0.5 and x = 5:
- At x = 0.5: Since 0 < 0.5 < 4, we use F(x) = x² / 16:
F(0.5) = (0.5)² / 16 = 0.25 / 16 = (1/4) / 16 = 1 / 64 (or 0.015625)
- At x = 5: Since x = 5 ≥ 4, the cumulative probability reaches its maximum value:
F(5) = 1
Question 26
Problem: Given the probability mass function of a discrete random variable X as P(X = x) = 4Cx (5/9)x (4/9)4-x for x = 0, 1, 2, 3, 4 (and 0 otherwise), calculate the expected value E(X) and variance Var(X).
Solution:
Given p.m.f.:
P(X = x) = 4Cx (5/9)x (4/9)4-x, for x = 0, 1, 2, 3, 4
Comparing this with the standard Binomial distribution formula P(X = x) = nCx px qn-x, we identify that X follows a Binomial distribution B(n, p) with:
- Number of trials, n = 4
- Probability of success, p = 5/9
- Probability of failure, q = 4/9
1. To find E(X):
For a binomial distribution, the mean or expected value is given by:
E(X) = n · p
E(X) = 4 × (5/9)
E(X) = 20 / 9
2. To find Var(X):
For a binomial distribution, the variance is given by:
Var(X) = n · p · q
Var(X) = 4 × (5/9) × (4/9)
Var(X) = 80 / 81
Section D
Question 27
Problem: Find the inverse of the matrix:
| [ -4 | -3 | -3 ] |
| [ 1 | 0 | 1 ] |
| [ 4 | 4 | 3 ] |
Solution:
Let the given matrix be A:
| [ -4 | -3 | -3 ] |
| [ 1 | 0 | 1 ] |
| [ 4 | 4 | 3 ] |
Step 1: Find the determinant |A|
|A| = -4(0 × 3 - 1 × 4) - (-3)(1 × 3 - 1 × 4) + (-3)(1 × 4 - 0 × 4)
|A| = -4(0 - 4) + 3(3 - 4) - 3(4 - 0)
|A| = -4(-4) + 3(-1) - 3(4)
|A| = 16 - 3 - 12 = 1 ≠ 0
Since |A| ≠ 0, the matrix A is non-singular and A-1 exists.
Step 2: Find the cofactors of the elements of matrix A
- A11 = (-1)1+1 (0 - 4) = -4
- A12 = (-1)1+2 (3 - 4) = -(-1) = 1
- A13 = (-1)1+3 (4 - 0) = 4
- A21 = (-1)2+1 (-9 - (-12)) = -(3) = -3
- A22 = (-1)2+2 (-12 - (-12)) = 0
- A23 = (-1)2+3 (-16 - (-12)) = -(-4) = 4
- A31 = (-1)3+1 (-3 - 0) = -3
- A32 = (-1)3+2 (-4 - (-3)) = -(-1) = 1
- A33 = (-1)3+3 (0 - (-3)) = 3
The matrix of cofactors [Aij] is:
| [ -4 | 1 | 4 ] |
| [ -3 | 0 | 4 ] |
| [ -3 | 1 | 3 ] |
Step 3: Find the adjoint of matrix A
adj(A) is the transpose of the cofactor matrix:
| [ -4 | -3 | -3 ] |
| [ 1 | 0 | 1 ] |
| [ 4 | 4 | 3 ] |
Step 4: Find the inverse A-1
Using the formula A-1 = (1 / |A|) · adj(A):
A-1 = (1 / 1) · adj(A)
Therefore, A-1 is:
| [ -4 | -3 | -3 ] |
| [ 1 | 0 | 1 ] |
| [ 4 | 4 | 3 ] |
Question 28
Problem: Prove that the homogeneous equation of degree two in x and y, ax² + 2hxy + by² = 0, represents a pair of lines passing through the origin if h² - ab ≥ 0.
Solution:
Consider the homogeneous equation of degree two in x and y:
ax² + 2hxy + by² = 0 — (Equation 1)
In this second-degree equation, the coefficients a, h, and b cannot all be zero simultaneously. We consider two cases based on the value of b:
Case 1: When b = 0
If b = 0, then a and h cannot both be zero. Substituting b = 0 into Equation 1 gives:
ax² + 2hxy = 0
x(ax + 2hy) = 0
This gives two linear equations:
x = 0 and ax + 2hy = 0
Since both are first-degree equations in x and y with no constant term, they represent two straight lines passing through the origin.
Case 2: When b ≠ 0
Multiply both sides of Equation 1 by b:
abx² + 2hbxy + b²y² = 0
b²y² + 2hbxy = -abx²
To complete the square on the left-hand side, add h²x² to both sides:
b²y² + 2hbxy + h²x² = h²x² - abx²
(by + hx)² = (h² - ab)x²
Given that h² - ab ≥ 0, we can write (h² - ab) = [√(h² - ab)]²:
(hx + by)² - [x√(h² - ab)]² = 0
Factoring using a² - b² = (a + b)(a - b):
[ (hx + by) + x√(h² - ab) ] [ (hx + by) - x√(h² - ab) ] = 0
[ (h + √(h² - ab))x + by ] [ (h - √(h² - ab))x + by ] = 0
This equation is the combined equation of the two lines:
- (h + √(h² - ab))x + by = 0
- (h - √(h² - ab))x + by = 0
Since both equations are linear in x and y and lack constant terms, they represent a pair of straight lines passing through the origin.
Hence proved.
Question 29
Problem: Prove that, if a, b, c are three non-coplanar vectors, then any vector r in space can be uniquely expressed as a linear combination of a, b, c.
Solution:
Part 1: Existence of the Linear Combination
Let a, b, c be three non-coplanar vectors in space, and let r be any arbitrary vector in space.
Take a fixed point O in space as the origin. Let the vectors a, b, c, and r be positioned along the directed line segments from O such that OP = r, and the lines along a, b, and c pass through O.
Through point P, draw planes parallel to the planes determined by the pairs of vectors (b, c), (c, a), and (a, b). Let these planes intersect the lines containing a, b, and c at points A, B, and C respectively, forming a parallelepiped with OP as its diagonal and OA, OB, OC as its coterminous edges.
- Since OA is collinear with a, there exists a scalar x ∈ R such that OA = xa.
- Since OB is collinear with b, there exists a scalar y ∈ R such that OB = yb.
- Since OC is collinear with c, there exists a scalar z ∈ R such that OC = zc.
By the parallelepiped law of vector addition:
OP = OA + OB + OC
r = xa + yb + zc
Thus, the vector r can be expressed as a linear combination of a, b, and c.
Part 2: Uniqueness of the Representation
Suppose the vector r can also be expressed as another linear combination of a, b, and c using scalars x', y', z':
r = x'a + y'b + z'c
Equating the two expressions for r:
xa + yb + zc = x'a + y'b + z'c
(x - x')a + (y - y')b + (z - z')c = 0
Since a, b, and c are three non-coplanar vectors, they are linearly independent. If any scalar coefficient were non-zero (for example, if x - x' ≠ 0), we could express a as a linear combination of b and c, which would contradict the fact that a, b, and c are non-coplanar.
Therefore, all coefficients must equal zero:
- x - x' = 0 ⇒ x = x'
- y - y' = 0 ⇒ y = y'
- z - z' = 0 ⇒ z = z'
Hence, the linear combination is unique.
Hence proved.
Question 30
Problem: Solve the linear programming problem (L.P.P.) by graphical method:
Minimize: z = 8x + 10y
Subject to:
- 2x + y ≥ 7
- 2x + 3y ≥ 15
- x ≥ 0
- y ≥ 2
Solution:
Step 1: Convert the given inequations into equations to plot the boundary lines
| Inequation | Equation of Line | Points on the Line | Origin Test (0, 0) | Feasible Half-Plane |
|---|---|---|---|---|
| 2x + y ≥ 7 | 2x + y = 7 (L1) | (0, 7), (3.5, 0) | 0 ≥ 7 (False) | Non-origin side of L1 |
| 2x + 3y ≥ 15 | 2x + 3y = 15 (L2) | (0, 5), (7.5, 0) | 0 ≥ 15 (False) | Non-origin side of L2 |
| y ≥ 2 | y = 2 (L3) | (0, 2), line parallel to X-axis | 0 ≥ 2 (False) | Non-origin side (above y = 2) |
| x ≥ 0 | x = 0 (Y-axis) | Along Y-axis | — | Right side of Y-axis |
Step 2: Determine the corner points of the feasible region
Plotting the lines and shading the common region in the first quadrant gives an unbounded feasible region with vertices A, B, and C:
- Point A: Intersection of x = 0 and 2x + y = 7:
Substituting x = 0 gives y = 7. Thus, A = (0, 7).
- Point B: Intersection of 2x + y = 7 and 2x + 3y = 15:
Subtracting (2x + y = 7) from (2x + 3y = 15) gives 2y = 8 ⇒ y = 4.
Substituting y = 4 into 2x + y = 7 gives 2x + 4 = 7 ⇒ 2x = 3 ⇒ x = 1.5 (or 3/2).
Thus, B = (1.5, 4).
- Point C: Intersection of 2x + 3y = 15 and y = 2:
Substituting y = 2 into 2x + 3y = 15 gives 2x + 6 = 15 ⇒ 2x = 9 ⇒ x = 4.5 (or 9/2).
Thus, C = (4.5, 2).
Step 3: Evaluate the objective function z = 8x + 10y at the corner points
| Corner Point | Coordinates (x, y) | Value of z = 8x + 10y |
|---|---|---|
| A | (0, 7) | z = 8(0) + 10(7) = 0 + 70 = 70 |
| B | (1.5, 4) | z = 8(1.5) + 10(4) = 12 + 40 = 52 (Minimum) |
| C | (4.5, 2) | z = 8(4.5) + 10(2) = 36 + 20 = 56 |
Conclusion: The minimum value of z is 52, which occurs at the point x = 1.5 (or 3/2) and y = 4.
Question 31
Problem: If x = f(t) and y = g(t) are differentiable functions of t, so that y is a differentiable function of x and dx/dt ≠ 0, then prove that dy/dx = (dy/dt) / (dx/dt). Hence find dy/dx, if x = sin t and y = cos t.
Solution:
Part 1: Proof of Parametric Differentiation Theorem
Let x = f(t) and y = g(t) be differentiable functions of a parameter t.
Let δt be a small increment in t, and let δx and δy be the corresponding small increments in x and y respectively, such that δx ≠ 0. As δt → 0, we have δx → 0 and δy → 0.
Since x and y are differentiable functions of t:
limδt → 0 (δx / δt) = dx/dt and limδt → 0 (δy / δt) = dy/dt
Consider the increment ratio:
δy / δx = (δy / δt) / (δx / δt), where (δx / δt) ≠ 0
Taking the limit as δt → 0 on both sides:
limδt → 0 (δy / δx) = [ limδt → 0 (δy / δt) ] / [ limδt → 0 (δx / δt) ]
Since δx → 0 as δt → 0, and y is a differentiable function of x, the left-hand side limit exists and equals dy/dx:
limδx → 0 (δy / δx) = (dy/dt) / (dx/dt)
dy/dx = (dy/dt) / (dx/dt), where dx/dt ≠ 0
Hence proved.
Part 2: To find dy/dx when x = sin t and y = cos t
Given: x = sin t and y = cos t
Differentiating both with respect to t:
- dx/dt = d/dt (sin t) = cos t
- dy/dt = d/dt (cos t) = -sin t
Using the parametric differentiation formula:
dy/dx = (dy/dt) / (dx/dt)
dy/dx = -sin t / cos t
dy/dx = -tan t
Question 32
Problem: Evaluate: ∫ [ 2 / (3 + 2sin²x + 5cos²x) ] dx
Solution:
Let I = ∫ [ 2 / (3 + 2sin²x + 5cos²x) ] dx
Divide both the numerator and the denominator by cos²x:
I = ∫ [ (2 / cos²x) / ( (3 / cos²x) + 2(sin²x / cos²x) + 5(cos²x / cos²x) ) ] dx
I = ∫ [ 2sec²x / (3sec²x + 2tan²x + 5) ] dx
Use the trigonometric identity sec²x = 1 + tan²x in the denominator:
I = ∫ [ 2sec²x / (3(1 + tan²x) + 2tan²x + 5) ] dx
I = ∫ [ 2sec²x / (3 + 3tan²x + 2tan²x + 5) ] dx
I = ∫ [ 2sec²x / (5tan²x + 8) ] dx
Substitute tan x = t.
Differentiating with respect to x gives: sec²x dx = dt.
Substitute into the integral I:
I = ∫ [ 2 / (5t² + 8) ] dt
I = (2 / 5) ∫ [ 1 / (t² + 8/5) ] dt
I = (2 / 5) ∫ [ 1 / (t² + (√(8/5))²) ] dt
Using the standard integration formula ∫ [ 1 / (x² + a²) ] dx = (1 / a) tan-1(x / a) + C:
I = (2 / 5) · [ 1 / √(8/5) ] tan-1[ t / √(8/5) ] + C
I = (2 / 5) · ( √5 / 2√2 ) tan-1( √5 t / 2√2 ) + C
I = ( 1 / √10 ) tan-1( √5 t / 2√2 ) + C
Resubstituting t = tan x:
I = ( 1 / √10 ) tan-1[ ( √5 tan x ) / ( 2√2 ) ] + C
Where 'C' is the constant of integration.
Question 33
Problem: Prove that:
∫-aa f(x) dx = 2 ∫0a f(x) dx, if f(x) is an even function
∫-aa f(x) dx = 0, if f(x) is an odd function
Solution:
Since -a < 0 < a, by the additive property of definite integrals, we can split the integral at 0:
∫-aa f(x) dx = ∫-a0 f(x) dx + ∫0a f(x) dx — (Equation 1)
Consider the first integral on the right-hand side:
I1 = ∫-a0 f(x) dx
Put x = -t. Differentiating with respect to t gives dx = -dt.
Changing the limits of integration:
- When x = -a, t = a
- When x = 0, t = 0
Substituting into I1:
I1 = ∫a0 f(-t) (-dt) = -∫a0 f(-t) dt
Using the property -∫ab g(t) dt = ∫ba g(t) dt:
I1 = ∫0a f(-t) dt
Since a definite integral is independent of the variable of integration (∫0a f(-t) dt = ∫0a f(-x) dx):
I1 = ∫0a f(-x) dx
Substituting I1 back into Equation 1:
∫-aa f(x) dx = ∫0a f(-x) dx + ∫0a f(x) dx
∫-aa f(x) dx = ∫0a [ f(-x) + f(x) ] dx — (Equation 2)
Case 1: If f(x) is an even function
By definition of an even function, f(-x) = f(x). Substituting this into Equation 2:
∫-aa f(x) dx = ∫0a [ f(x) + f(x) ] dx
∫-aa f(x) dx = 2 ∫0a f(x) dx
Case 2: If f(x) is an odd function
By definition of an odd function, f(-x) = -f(x). Substituting this into Equation 2:
∫-aa f(x) dx = ∫0a [ -f(x) + f(x) ] dx
∫-aa f(x) dx = 0
Hence proved.
Question 34
Problem: A body cools according to Newton's law from 100°C to 60°C in 20 minutes. The temperature of the surrounding being 20°C. How long will it take to cool down to 40°C?
Solution:
Let θ be the temperature of the body at time t minutes. The temperature of the surrounding medium is θ0 = 20°C.
According to Newton's Law of Cooling, the rate of change of temperature is directly proportional to the difference between the temperature of the body and the surrounding medium:
dθ/dt ∝ -(θ - θ0)
dθ/dt = -k(θ - 20), where k > 0 is the constant of proportionality.
Separating the variables:
[ 1 / (θ - 20) ] dθ = -k dt
Integrating both sides:
∫ [ 1 / (θ - 20) ] dθ = -k ∫ dt
log(θ - 20) = -kt + c — (Equation 1)
Step 1: Find the constant c using the initial condition
Initially, at t = 0, θ = 100°C. Substituting into Equation 1:
log(100 - 20) = -k(0) + c
c = log 80
Substituting c = log 80 back into Equation 1:
log(θ - 20) = -kt + log 80
log(θ - 20) - log 80 = -kt
log[ (θ - 20) / 80 ] = -kt — (Equation 2)
Step 2: Find the value of -k using the second condition
Given that at t = 20 minutes, θ = 60°C. Substituting into Equation 2:
log[ (60 - 20) / 80 ] = -20k
log(40 / 80) = -20k
log(1 / 2) = -20k
-k = (1 / 20) log(1 / 2)
Substituting -k into Equation 2 gives:
log[ (θ - 20) / 80 ] = (t / 20) log(1 / 2) — (Equation 3)
Step 3: Find time t when θ = 40°C
Substitute θ = 40 into Equation 3:
log[ (40 - 20) / 80 ] = (t / 20) log(1 / 2)
log(20 / 80) = (t / 20) log(1 / 2)
log(1 / 4) = (t / 20) log(1 / 2)
log[ (1 / 2)² ] = (t / 20) log(1 / 2)
2 log(1 / 2) = (t / 20) log(1 / 2)
Dividing both sides by log(1 / 2):
2 = t / 20
t = 40 minutes
Conclusion: It will take 40 minutes in total for the body to cool down to 40°C.
HSC 12th Maths June 2026 Board Question Paper (J-276) – Original Images
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